Secretary IgA (SIgA) is the predominate form of antibody that mediates specific immunological defence at mucosal surfaces (1). Protection is afforded by several recognised mechanisms; interfering with microbial adherence to mucosal surfaces, inhibiting penetration of antigens across the epithelial membrane, complexing with antigens at the basolateral surface of the mucosal epithelium to facilitate elimination by exocytosis into the mucosal lumen, and salvage mechanisms at intracellular and interstitial levels (2). In humans, immunoglobulin A (IgA) occurs as two subclasses that differs in amino acid sequences and glycosylation of the alpha heavy chain (3). IgA1 predominates (approximately 90%) in serum, whereas IgA2 predominates in most mucosal secretions (4). The proportions of the two subclasses vary between mucosal sites due to differences in the distribution of immunoglobulin producing immunocytes (1,5–6). Saliva contains approximately 60% IgA1 in normal adults (4,7–8).
Research into salivary IgA levels in exercising populations has received considerable attention due to reports of a high prevalence of respiratory infections in elite athletes (9–12). The associations between changes in salivary IgA concentrations with exercise are complex and depend on the intensity, duration and periodicity of training and degree of fitness of the athlete (13–14). Salivary IgA concentrations have been shown to be reduced after intense exercise in the elite athletes training in a variety of endurance sports (14–19). The only report of the influence of exercise on IgA subclasses has been a study of maximal exercise on total IgA and IgA subclasses in human breastmilk (20). In the breastmilk, total IgA and IgA1 but not IgA2 concentrations were decreased after exhaustive exercise, with recovery to baseline levels within 60 minutes (20).
Recently it was reported that low concentrations of IgA in saliva of elite swimmers and a moderately exercising group were associated with an increased risk of respiratory infection (16). Longitudinal studies with elite swimmers have also shown a significant decline in salivary IgA concentrations over a 7-month training season (15–16). However, not all swimmers undertaking the training program were susceptible to infection.
There remains a need for a suitable and timely test to predict susceptibility to infection in subjects exposed to physical or other stress.
It is an object of the present invention to overcome or ameliorate at least some of the disadvantages of the prior art, or to provide a useful alternative.